1. Field of the Invention
The present invention pertains to the field of imaging. More particularly, the present invention relates to a system of imaging that utilizes a plurality of image collection hardware elements that can be selectively employed to give a desired image configuration for a desired imaging technique.
2. Discussion of the Background
The prior art demonstrates a number of techniques used for image processing. These techniques involve configuring and then reconfiguring an image to achieve an improved image, i.e., an image reconfiguration.
For example, it is well established that contrast is reduced when a scene is viewed through a medium with suspended particles in it, but contrast can be enhanced by viewing the scene through two orthogonal polarizations, then taking the difference between the two polarized scenes. Taking the difference between the two polarizations has the effect of reducing the scattering, thus enhancing the contrast. The medium could be the earth's atmosphere filled with dust, or aerosols or a piece of biological tissue viewed through a microscope. U.S. Pat. No. 5,975,702 to Pugh, Jr. et al. that issued Nov. 2, 1999 and which is herein incorporated by reference demonstrates this method of polarization differencing.
The ability to collect a large number of narrow hyperspectral images of the same scenes allows one to then select the best set of a smaller number of bands that give the best signal to noise ratio, and the bands need not may be contiguous.
A well established art in the field of hyperspectral imaging has been made possible by the voltage controlled acousto-optical tunable filter. The imagery that can be collected through such tunable filters can be quite varied—from topographical scenes to the imaging of biological specimens.
Acousto-optic tunable filters (AOTF's) are taught in U.S. Pat. No. 4,720,177, U.S. Pat. No. 4,685,772 and U.S. Pat. No. 5,329,397 to Chang which issued on Jan. 19, 1988, Aug. 11, 1987, and Jul. 12, 1994, respectively, the teachings of which are herein incorporated by reference. In U.S. Pat. No. 5,576,880 that issued Nov. 19, 1996, and which is herein incorporated by reference as well, Chang teaches an acoustic-optic modulator. AOTF's are used in a variety of imaging and display systems. An example of a display system utilizing an AOTF is U.S. Pat. No. 5,410,371 to Lambert which issued on Apr. 25, 1995, the teachings of which are herein incorporated by reference.
Another imaging technique has been to obtain an in-focus image and an out-of-focus image and then subtract the out-of-focus image from the in-focus image to obtain an enhanced image by removing the lower frequency components. This concept is disclosed in U.S. Pat. No. 6,433,325 to Trigg which issued on Aug. 13, 2002 the teachings of which are herein incorporated by reference. FIG. 1 demonstrates an embodiment from the Trigg patent in which a microscope body 18 having an optically aligned lens 14 and focal array 16 is operably connected to a ball screw assembly 20 that is driven by a motor 22 and controlled by a computer 24. A sample 12 resting on a sample stage 10 can be brought in and out of focus by the operation of the ball screw assembly.
The highest frequency component that can be captured in a focal plane array is limited by the detector pitch, or the spacing between the centers of the pixel elements. Under the Nyquist criteria, the highest frequency that a band-limited spectra can contain to be fully recoverable is one half the sampling rate, which in the case of the staring focal plane array is one half of the detector pitch.
Since infrared scenes typically contain frequencies higher than one half the sampling rate of the focal plane array, the result is aliasing, or the overlap of adjacent spectra leading to distortion of the sampled signals and the loss of information in the reconstruction process.
The reduction in distortion from aliasing can be achieved by a process of microscanning that shifts the image plane a fraction of the detector pitch in two coordinates over the focal plane array. This technique allows the capture of higher frequency components in an image that would otherwise be lost in distortion. The technique is presented in U.S. Pat. No. 5,774,179 to Chevrette et al. that issued on Jun. 30, 1998, the teachings of which are hereby incorporated by reference.
To establish some measure of quality of an image, a conceptual ruler or metric is needed. One commonly used metric in image analysis that has been used is the peak signal to noise ratio (PSNR).
If one image is defined as the reference image, then the degree of dissimilarity with a comparison image is given in terms of a distance measure or error. The most obvious measure of distance between two images is obtained by comparing them on a pixel-by-pixel basis and taking the difference between the pixel values (pixel difference metrics). For example, if a sensor device collects an image and it is compressed for transmission, and then decompressed, the decompressed image will differ from the original image by the errors or artifacts introduced by the compression-decompression process.
The variety of image similarity metrics previously used in imaging technology, has included spectral angle mapping, Euclidian distance and others. These metrics have ambiguities, and efforts have been made to improve them with something called a “spectral similarity scale”. A method for determining spectral similarity is disclosed in U.S. Pat. No. 6,763,136 that issued to Sweet on Jul. 13, 2004 which is hereby incorporated by reference.
In that the type of image that is desired and the circumstances and conditions under which an image is obtained can vary greatly, a need is seen for an image analysis and enhancement system that has the ability to utilize a multiplicity of imaging techniques positioned at local and/or remote locations.